S. Venkateswarlu et al. / Tetrahedron 63 (2007) 6909–6914
6913
5.70%. HRMS (m/z) Found: 266.1184, calcd for C17H15NO2
(M+H): 266.1181.
mp 98–100 ꢀC; IR (Neat): 1681, 1629, 1605, 1262, 1181,
1080, 1027, 961, 895 cmꢁ1 1H NMR (CDCl3): d 8.23
;
(2H, d, J¼8.8 Hz, H-20,60), 7.78 (1H, d, J¼8.0 Hz, H-4),
7.60 (1H, t, J¼8.0 Hz, H-6), 7.19 (1H, d, J¼8.0 Hz, H-7),
7.16 (1H, t, J¼8.0 Hz, H-5), 6.95 (2H, d, J¼8.8 Hz,
H-30,50), 6.93 (1H, s, H-10), 3.86 (3H, s, Ar–OCH3); 13C
NMR (CDCl3): d 182.5 (C-3), 165.0 (C-8), 161.6 (C-40),
147.1 (C-2), 136.3 (C-6), 133.1 (C-20,60), 124.9 (C-10),
124.5 (C-5), 123.7 (C-9), 123.2 (C-4), 122.5 (C-7), 114.0
(C-30,50), 112.5 (C-10), 55.4 (Ar–OCH3); LCMS (ESI,
positive scan): m/z 253 (M+H)+.
4.1.1.6. Z-2-[(4-Hydroxyphenyl)methylene]benzo[b]-
furan-3-one (1f). Light yellow powder, 167 mg (70%), mp
261–263 ꢀC; IR (KBr): 3431, 1686, 1642, 1612, 1288,
1173, 1132, 884 cmꢁ1 1H NMR (CDCl3+DMSO-d6): d
;
7.81 (2H, d, J¼8.4 Hz, H-20,60), 7.75 (1H, d, J¼7.6 Hz, H-4),
7.68 (1H, t, J¼7.6 Hz, H-6), 7.37 (1H, d, J¼7.6 Hz,
H-7), 7.23 (1H, t, J¼7.6 Hz, H-5), 6.93 (2H, d, J¼8.4 Hz,
H-30,50), 6.83 (1H, s, H-10); 13C NMR (CDCl3+DMSO-
d6): d 182.9, 164.5, 158.8, 144.2, 135.5, 132.6, 123.1,
122.3, 120.8, 115.3, 115.1, 112.8, 111.9; LCMS (ESI, nega-
tive scan): m/z 237 (MꢁH)ꢁ. Analysis found: C, 75.59; H,
4.25%. Calcd for C15H10O3: C, 75.62; H, 4.23%. HRMS
(m/z) Found: 239.0704, calcd for C15H10O3 (M+H):
239.0708.
4.1.2.4. E-2-[(3,4,5-Trimethoxyphenyl)methylene]-
benzo[b]furan-3-one (2d). Light yellow powder, 260 mg
(26%), mp 105–106 ꢀC; IR (Neat): 2940, 1688, 1630,
1601, 1299, 1244, 1190, 1127, 1085, 1005, 948, 867 cmꢁ1
;
1H NMR (CDCl3): d 7.80 (1H, d, J¼7.9 Hz, H-4), 7.68
(2H, s, H-20,60), 7.63 (1H, td, J¼7.9, 1.1 Hz, H-6), 7.21
(1H, d, J¼7.9 Hz, H-7), 7.18 (1H, t, J¼7.9 Hz, H-5), 6.92
(1H, s, H-10), 3.98 (6H, s, 2ꢂAr–OCH3), 3.93 (3H, s, Ar–
OCH3); 13C NMR (CDCl3): d 182.7 (C-3), 165.1 (C-8),
152.9 (C-30,50), 147.8 (C-2), 140.7 (C-40), 136.6 (C-20,60),
127.5 (C-10), 124.5 (C-6), 123.7 (C-5), 123.5 (C-9), 122.7
(C-4), 112.5 (C-10), 108.8 (C-7), 60.9 (Ar–OCH3), 56.3
(2ꢂAr–OCH3); LCMS (ESI, positive scan): m/z 313
(M+H)+. Analysis found: C, 69.22; H, 5.95%. Calcd for
C18H16O5: C, 70.79; H, 5.95%.
4.1.1.7. Z-2-[(3,4-Dihydroxyphenyl)methylene]benzo-
[b]furan-3-one (1g). Light yellow powder, 102 mg (40%),
mp 218–220 ꢀC; IR (KBr): 3441, 3278, 1697, 1649, 1585,
1
1295, 1189, 1132, 886 cmꢁ1; H NMR (CDCl3+DMSO-
d6): d 7.76 (d, J¼7.4 Hz, H-4), 7.66 (1H, t, J¼7.4 Hz,
H-6), 7.57 (1H, dd, J¼8.0, 1.2 Hz, H-60), 7.30–7.35 (2H, m,
H-7,20), 7.22 (1H, t, J¼7.4 Hz, H-5), 6.90–6.94 (1H, m, H-
50), 6.79 (1H, s, H-10); 13C NMR (CDCl3+DMSO-d6):
d 183.4, 164.8, 147.4, 144.6, 135.8, 124.6, 123.5, 123.3,
122.5, 121.2, 117.8, 117.4, 115.4, 113.7, 112.1; LCMS
(ESI, negative scan): m/z 253 (MꢁH)ꢁ. Analysis found: C,
70.82; H, 3.99%. Calcd for C15H10O4: C, 70.86; H, 3.96%.
Acknowledgements
4.1.2. General procedure for the preparation of E-aurones
(2). A solution of Z-aurones (1, 1.0 g) in methanol (500 mL)
was irradiated using Rayonet reactor at 350 nm for 12 h. The
solvent was evaporated under reduced pressure and the resi-
due was chromatographed over silica gel column using hex-
ane–ethyl acetate mixtures as eluents to give the E-aurones.
We sincerely thank Sri G. Ganga Raju, Chairman; Mr. G.
Rama Raju, Director, of Laila Impex for providing facilities
and encouragement; and Prof. A. Srikrishna, Indian Institute
of Science, Bangalore, India for helpful discussions.
References and notes
4.1.2.1. E-2-[(4-Chlorophenyl)methylene]benzo[b]-
furan-3-one (2a). Light yellow powder, 550 mg (55%),
1. Harborne, J. B. The Flavonoids; Chapman and Hall: London,
1988; pp 340–342.
2. Boumendjel, A. Curr. Med. Chem. 2003, 10, 2621–2630.
3. Varma, R. S.; Varma, M. Tetrahedron Lett. 1992, 33, 5937–
5940.
4. Lawrence, N. J.; Rennison, D.; McGown, A. T.; Hadfield, J. A.
Bioorg. Med. Chem. Lett. 2003, 13, 3759–3763.
5. Thakkar, K.; Cushman, M. J. Org. Chem. 1995, 60, 6499–6510.
6. Bose, G.; Mondal, E.; Khan, A. T.; Bordoloi, M. J. Tetrahedron
Lett. 2001, 42, 8907–8909.
7. Imafuku, K.; Honda, M.; McOmie, J. F. W. Synthesis 1987,
199–201.
8. Atta-Ur-Rahman; Choudhary, M. I.; Hayat, S.; Khan, A. M.;
Ahmed, A. Chem. Pharm. Bull. 2001, 49, 105–107.
9. Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J. P.
J. Am. Chem. Soc. 1985, 107, 3902–3909.
10. Zimmerman, H. E.; Ahramjian, L. J. Am. Chem. Soc. 1959, 81,
2086–2091.
11. Cragg, G. M.; Newman, D. J.; Yang, S. S. J. Nat. Prod. 2006,
69, 488–498.
mp 148–150 ꢀC; IR (Neat): 1686, 1630, 1589, 1237, 1197,
1
1081, 1018, 963, 896 cmꢁ1; H and 13C NMR (CDCl3):
see Table 3; LCMS (ESI, positive scan): m/z 257, 259
(M+H)+. Analysis found: C, 70.41; H, 3.66%. Calcd for
C15H9ClO2: C, 70.19; H, 3.53%.
4.1.2.2. E-2-[(4-Fluorophenyl)methylene]benzo[b]-
furan-3-one (2b). Light yellow powder, 510 mg (51%), mp
156–158 ꢀC; IR (Neat): 1688, 1620, 1600, 1240, 1165,
1
1082, 960, 897 cmꢁ1; H NMR (CDCl3): d 8.20 (2H, dd,
J¼8.6, 5.2 Hz, H-20,60), 7.77 (1H, d, J¼7.9 Hz, H-4), 7.61
(1H, td, J¼7.9, 1.1 Hz, H-6), 7.19 (1H, d, J¼7.9 Hz, H-7),
7.17 (1H, t, J¼7.9 Hz, H-5), 7.10 (2H, dd, J¼8.6 Hz,
H-30,50), 6.90 (1H, s, H-10); 13C NMR (CDCl3): d 182.7
(C-3), 165.3 (C-8), 163.8 (d, 1JCF¼250 Hz, C-40), 147.8 (C-
3
2), 136.8 (C-6), 133.1 (d, JCF¼9 Hz, C-20,60), 128.2 (d,
4JCF¼4 Hz, C-10), 124.6 (C-5), 123.3 (C-9), 122.8 (C-4),
2
121.4 (C-7), 115.5 (d, JCF¼22 Hz, C-30,50), 112.6 (C-10);
LCMS (ESI, positive scan): m/z 241 (M+H)+. Analysis found:
C, 75.06; H, 3.90%. Calcd for C15H9FO2: C, 75.00; H, 3.78%.
12. Venkateswarlu, S.; Panchagnula, G. K.; Guraiah, M. B.;
Subbaraju, G. V. Tetrahedron 2005, 61, 3013–3017.
13. Venkateswarlu, S.; Panchagnula, G. K.; Guraiah, M. B.;
Subbaraju, G. V. Tetrahedron 2006, 62, 9855–9860.
4.1.2.3. E-2-[(4-Methoxyphenyl)methylene]benzo[b]-
furan-3-one (2c). Light yellow powder, 600 mg (60%),